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perf/core: Add speculation info to branch entries

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Add a new "spec" bitfield to branch entries for providing speculation
information. This will be populated using hints provided by branch sampling
features on supported hardware. The following cases are covered:

  * No branch speculation information is available
  * Branch is speculative but taken on the wrong path
  * Branch is non-speculative but taken on the correct path
  * Branch is speculative and taken on the correct path

Suggested-by: Stephane Eranian <eranian@google.com>
Signed-off-by: Sandipan Das <sandipan.das@amd.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/834088c302faf21c7b665031dd111f424e509a64.1660211399.git.sandipan.das@amd.com
This commit is contained in:
Sandipan Das 2022-08-11 18:00:00 +05:30 committed by Peter Zijlstra
parent 245268c19f
commit 93315e46b0
2 changed files with 15 additions and 1 deletions
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1
include/linux/perf_event.h
View File

@ -1078,6 +1078,7 @@ static inline void perf_clear_branch_entry_bitfields(struct perf_branch_entry *b
br->abort = 0;
br->cycles = 0;
br->type = 0;
br->spec = PERF_BR_SPEC_NA;
br->reserved = 0;
}

15
include/uapi/linux/perf_event.h
View File

@ -256,6 +256,17 @@ enum {
PERF_BR_MAX,
};
/*
* Common branch speculation outcome classification
*/
enum {
PERF_BR_SPEC_NA = 0, /* Not available */
PERF_BR_SPEC_WRONG_PATH = 1, /* Speculative but on wrong path */
PERF_BR_NON_SPEC_CORRECT_PATH = 2, /* Non-speculative but on correct path */
PERF_BR_SPEC_CORRECT_PATH = 3, /* Speculative and on correct path */
PERF_BR_SPEC_MAX,
};
#define PERF_SAMPLE_BRANCH_PLM_ALL \
(PERF_SAMPLE_BRANCH_USER|\
PERF_SAMPLE_BRANCH_KERNEL|\
@ -1363,6 +1374,7 @@ union perf_mem_data_src {
* abort: aborting a hardware transaction
* cycles: cycles from last branch (or 0 if not supported)
* type: branch type
* spec: branch speculation info (or 0 if not supported)
*/
struct perf_branch_entry {
__u64 from;
@ -1373,7 +1385,8 @@ struct perf_branch_entry {
abort:1, /* transaction abort */
cycles:16, /* cycle count to last branch */
type:4, /* branch type */
reserved:40;
spec:2, /* branch speculation info */
reserved:38;
};
union perf_sample_weight {